LESSON 3.1: Direct Fecal Smear (DFS) and Cellulose Tape Swab (CTS)

Examination of Fecal Specimen

presence of parasites with intestinal origin is primarily identified through direct examination of stool

Wet mounts; Concentration techniques; Permanently stained smear; Culture

Methods of stool examination

Intestinal protozoan infections

diagnosed by the detection of trophozoites, cysts, or oocysts

Ova and Parasites (O&P examination)

procedures that permit the recovery of both protozoan and helminths

three (3) specimens collected every other day (3 specimens within 10 days)

Minimum collection of O&P specimens

up to seven (7) O&P examinations

Giardia lamblia and Strongyloides stercoralis detection collection

Wet mounts

small amount of stool only; detect motile trophozoites, cyst, ova, and larvae; rapid initial diagnosis

Concentration techniques

improve the sensitivity of the stool examination; increased chance of detecting cyst, eggs, and larvae

Permanently stained smear

Involves smearing, fixation, and staining; detailed microscopic study of protozoan morphology

Culture

use to let parasite grow and multiply; increase detection; used in research and studies

6 specimens within 14 days

Amebiasis (entamoeba histolytica) collection

30 mins to 1 hour after passage

Age of sample (diarrheic specimen)

24 hours

Age of sample (formed stool)

3–5°C

Storage temperature

Gross Examination; Fecal Techniques; Microscopic Techniques

Phases in studying stool sample

3–5 g (2–5 g in other references); thumb sized or pea sized

Specimen size

Specimen container

clean, dry, waterproof, wide

Color; Consistency; presence of parasitic forms

Macroscopic Examination

RBC; WBC; Fat globules; Bacteria; Parasites

Microscopic Examination

Name; Birthdate; Date and time of collection

Specimen label

Upper GI bleeding; Iron therapy; Charcoal; Bismuth

Black stool presents

Lower GI bleeding; Beets; food coloring; Rifampin

Red stool presents

Bile duct obstruction; Barium sulfate

Pale yellow/white/gray stool presents

Biliverdin/oral antibiotics; Green vegetables

Green stool presents

Bile duct obstruction; Pancreatic disorders

Bulky/forthy stool presents

Intestinal constriction

Ribbon like stool presents

Colitis; Dysentery; Malignancy; Constipation

Mucus or blood streaked mucus presents

Upper GI bleeding (melena)

blood digested; black stool

Lower GI bleeding (hematochezia)

blood not digested; bright red stool

None (fresh stool); 10% formalin; Schaudinn’s fluid; Polyvinyl alcohol (PVA); Modified PVA; Merthiolate iodine formalin (MIF); Sodium acetate formalin (SAF)

Stool fixatives

DWM, CP, PSS

Examination Techniques involve in Fresh Stool

DWM, CP

Examination Techniques involve in Formalin

PSS

Examination Techniques involve in Schaudinn’s fluid

PSS

Examination Techniques involve in PVA and Modified PVA

DWM, CP

Examination Techniques involve in MIF

DWM, CP, PSS

Examination Techniques involve in SAF

10% concentration

preserve helminth eggs

5% concentration

preserve cysts

Formalin

does not preserve morphology of the parasite

Schaudinn’s fluid and PVA

contains mercury (toxic)

Modified PVA

contains zinc sulfate or copper sulfate

SAF

less toxic; significant for modified acid fast stain (used for oocyst)

Direct Fecal Smear (DFS)

Wet Smear Preparation; Iodine Smear Preparation

perform gross examination; add NSS; emulsify stool; cover slip; observe under LPO and HPO

Wet Smear Preparation steps

0.85% concentration

Concentration of Normal saline solution (NSS)

3 × 2 inches

Glass slide size

22 mm

Cover slip size

Comminuted

stool sample is finely broken down or crushed into very small pieces

Iodine Smear Preparation

add Lugol’s iodine; visualization of cyst; trophozoite dies

Lugol’s iodine

D’Antoni’s formula

detect motility of trophozoite or cyst

NSS function

Iodine

determine cyst (nucleus, morphology)

Cellulose Tape Swab (CTS)

Known as Scotch Tape Swab Method; Graham's Scotch Adhesive Tape swab

CTS

Gold standard for diagnosis of Enterobius vermicularis

3 consecutive days early morning before bath or washing perineum

CTS collection time

10–11 pm after patient has slept

Alternative collection time

4–6 consecutive negative tapes (or 5)

Negative result requirement

eggs of Taenia spp. and Schistosoma mansoni

CTS may additionaly recover

female Enterobius vermicularis migrates out of the anus at night and deposits eggs over the perianal area; eggs adhere to cellophane tape

CTS principle

Enterobius vermicularis Ova/egg

elongated, flattened on one side; football

Egg structure

double layered (albuminous layer and lipoidal layer); no glycogen

4–6 hours

Embryonated egg infective time

resistant to disinfectant; succumb to desiccation in dry air

Resistance of E. vermicularis

2½ to 3 inches

CTS tape length

CTS procedure steps

apply tape; obtain sample; press on perianal folds; replace tape; add toluene; examine under LPO

Toluene

clears everything except the eggs and female adults